Method for increasing brake efficiency

ABSTRACT

Within the framework of the method for increasing brake efficiency of a vehicle with a hydrodynamic retarder, the rotational speed of the motor is increased by command for downshifting, in such a manner, that the increased cooling fluid circulation flow, due to the higher rotational speed of the motor speed, the necessary retarder braking power is made available, whereby a downshift command is issued, if this is necessary due to the actual retarder braking power.

FIELD OF THE INVENTION

The present invention concerns a method for increasing the brakingefficiency of a vehicle using a hydrodynamic retarder.

BACKGROUND OF THE INVENTION

Retarders serve as a nearly abrasion free, lasting braking means,especially for commercial vehicles and rail guided vehicles, sincewithout abrasive wear retarders possess, for a long period, theadvantage of converting braking energy into heat.

In the case of hydrodynamic retarders, the fluid flow energy of a liquidis used for braking, wherein the physical active principle correspondsto that of a hydrodynamic clutch. In accord with this, the retarderdevelops a rotor-stator relationship in the power fluid, the said statorbeing immovably affixed in a retarder housing. Upon activation of theretarder, a quantity of oil, commensurate with the desired brakingpower, is admitted into the rotor blade space whereby the rotor carriesthe oil with it. The oil reacts thereupon against the stator, givingrise to a braking action which restrains the rotor shaft.

As a result of the above principle, it is possible that a retarder willproduce, at a low rotational speed, only a small braking moment.

Under normal driving conditions, the motor rotational speeds lie at arelatively low level, namely, within that rotational speed which is mostfavorable to the current use. Upon retarder braking, however, a greatercirculation of cooling fluid is required and, to this end, a highermotor rotational speed is both desired and necessary for optimaloperation.

On this account, the purpose of the present invention is to makeavailable a method which enables, even at originally low rotationalspeeds, the achievement of a sufficient desired retarder braking power.

SUMMARY OF THE INVENTION

In accordance with the above, the proposal is to increase the rotationalspeed by means of a command for a downshift issued by the retarder, insuch a manner, that by means of the higher motor rotational speed, thecirculating quantity of cooling fluid provides the necessary retarderbraking action. By means of increasing of the rotation rate of themotor, and because of the higher gear ratio, the entire braking powerresponse of the vehicle is increased.

In accordance with the invention, on the basis of comfort, only adownshift is carried out when such a shift is necessary because of theactual retarder braking power.

Within the framework of a variant, the entire situation is pre-analyzedand, in the case of necessity, a downshift command is released.

The determination as to whether or not a downshift is necessary, for thestepping of the actual potential for power of the retarder brakingsystem, is made by several mutually interacting characteristic values.

The retarder presents important criterion as to the actual brakingeffect of the retarders, which can be determined from the actual brakingmoment, the actual braking power, the retarder engagement ordisengagement, or the control flow.

Added thereto is the determination of further criterion of the actualdriving condition, which is arrived at from the actual rotary motorspeeds of the output shaft of the transmission, the wheels, the motorand the clutch, further thereto the speed of the vehicle, variations inthe RPM or the speed, characteristics of the topography or the weight ofthe vehicle relative to the said topography are required.

In accordance with the invention, also the capability of the vehiclecooling system to meet power commands which is obtainable, for example,from the temperature in the cooling system, its change as a function oftime, the pressure in the cooling fluid circuit, the current operatinggear position, the current clutch stage in operation and the RPM of thewater pump ust be taken into consideration for determination of adownshift.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic flow plan of the method according to thepresent invention; and,

FIG. 2 is a block diagram and flow diagram of a vehicle retarder brakingsystem in which the present invention may be implemented.

In accord with the invention, the above itemized and variouscharacteristic quantities are given consideration by a logicalcorrelation or with the aid of fuzzy computation, in order to recognizethe necessity of the command for a downshift and to allow this to bereleased.

An essential advantage of the use of fuzzy computation is to be found inthat different quantities are included in the final result in accordwith appropriate weighting.

The downshift command is conveyed to the driver acoustically, opticallyor by a sense of feel. Again, for an automatic shift system, the saidcommand can be automatically forwarded to effect the release of a shift.

In the framework of further variants, with the invented method, thenecessity of a downshift command, in the presence of an overstepping orunderstepping of a threshold value, can be recognized. Appropriatethreshold values can be established for cooling fluid temperature orgradients thereof, the rotational speed of the motor or gradientsthereof, rotational speed of the drive takeoff shaft or gradientsthereof.

Further, in the framework of an additional embodiment, the furtherdevelopment of the cooling fluid temperature and further optional valuescan be determined from a simulation of the cooling system. Based on thefindings thereof, a down shift can be commanded.

Likewise, it is possible, under condition of automatic braking, torelease a braking command, insofar as the retarder in the actualoperating conditions can obtain access to the required braking power andhence the braking moment.

1. A method for increasing brake efficiency of a vehicle with ahydrodynamic retarder, in which a rotational speed of a motor isincreased by command for downshifting in such a manner that due to anincreased rotational speed of the motor, a quantity of availablecirculating cooling fluid is increase to facilitate necessary retarderbraking, the method comprising the steps of: (20A) determining anecessity (16N) of a downshift command (16) from at least one of anactual braking efficiency (22) of the retarder (16), a driving condition(24), and a potential for cower (26) of a vehicle cooling system (28);(20B) determining an actual braking efficiency (22) from at least one ofan actual braking moment (32), a braking power (34), a retarder inletpressure (36), a retarder outlet pressure (38) and a regulating flow(40); (20C) determining an actual driving condition (24) from at leastone of an actual transmission output shaft rotational speed (42), arotational wheel speed (44) of a wheel (46), a motor rotational speed(48) of motor (14), a clutch rotational speed (50) of a clutch (52), avehicle speed (54) of the vehicle (10) and also from at least one of achange in rotational speed (56), a change in the vehicle speed (58), atopography (60), and a weight (62) of the vehicle (10) with respect tothe topography (60); (20D) determining the potential for power (26) ofthe vehicle cooling system (28) by at least one of a temperature (64) ofthe cooling system (28), a change of temperature (66) of the coolingsystem (28), a function of time (66), the rotational speed (48) of themotor (14), a pressure (70) of the cooling circulation system (28), ashift position (72), a clutch state (74) and a rotational speed (76) ofa water pump (78); and, (20E) when the necessity of a downshift command(16N) is determined, issuing the downshift command (16); and (20F) inresponse to the issued command (16) for downshifting, increasing arotational speed (48) of the motor (14) in such a manner that a quantity(80) of available circulating cooling fluid (18) is increase tofacilitate necessary retarder (12) braking.
 2. The method according toclaim 1, further comprising the step of making the downshift commandknown to a driver by one of an acoustic signal, an optical signal and bya tactile signal.
 3. The method according to claim 1, further comprisingthe step of automatically forwarding the downshift command to one of anautomatic shifting system and automated shifting system for the releaseof the shift action.
 4. A method for increasing brake efficiency of avehicle with a hydrodynamic retarder, in which a rotational speed of amotor is increased by command for downshifting in such a manner that dueto an increased rotational speed of the motor, a quantity of availablecirculating cooling fluid is increase to facilitate necessary retarderbraking, the method comprising the steps of; determining a need for adownshift from at least one of an actual braking efficiency of theretarder, a driving condition, and a potential for power of a vehiclecooling system; upon determining the need for a downshift, issuing adownshift command to increase the rotational speed of the motor andincrease the quantity of available circulating cooling fluid forfacilitating the necessary retarder braking.
 5. The method according toclaim 4, further comprising the steps of: determining an actual brakingefficiency from at least one of an actual braking moment, a brakingpower, a retarder inlet pressure, a retarder outlet pressure and aregulating flow; determining an actual driving condition from at leastone of an actual transmission output shaft rotational speed, arotational wheel speed, a motor rotational speed, a clutch rotatoryspeed, a vehicle speed and also from at least one of a change inrotational speed, a change in the vehicle speed, a topography, and aweight of the vehicle with respect to the topography; and determiningthe potential for power of the vehicle cooling system by at least one ofa temperature of the cooling system, a change of temperature of thecooling system, a function of time, the rotational speed of the motor, apressure of the cooling circulation system, a shift position, a clutchstate and a rotational speed of a water pump.
 6. The method according toclaim 4, further comprising the step of making the downshift commandknown to a driver by one of an acoustic signal, an optical signal and atactile signal.
 7. The method according to claim 4, further comprisingthe step of automatically forwarding the downshift command to one of anautomatic shifting system and automated shifting system for the releaseof the shift action.